In one type of blow molding machine, such as shown in U.S. Pat. Nos. 3,767,747, 3,781,395 and 3,978,184, a preform is extruded downwardly and preform mold halves and final blow mold halves are shifted laterally or horizontally from a position underlying the extruder. Blow pins (calibration pins) are provided in association with the blow molds.
Among the objectives of the present invention are to provide a blow molding method and apparatus of the above-described type wherein the productivity is doubled in one complete cycle; wherein the method and apparatus can be readily adapted to existing machines; and wherein the same machine can make different containers simultaneously.
In accordance with the invention, extruder means provide extruded tubular plastic parisons to first and second horizontally movable blow mold assemblies. Each blow mold assembly includes two sets of blow molds, and each set comprises a pair of blow mold halves. The blow mold halves are closed about the tubular parisons and moved to one of two blow molding stations where a blow pin at the blow molding station blows the parison to form a hollow blow molded article. More specifically, four platens are provided in each blow mold assembly. A first pair of outer and inner platens supports the first pair of blow mold halves and a second pair of outer and inner platens supports the second pair of blow mold halves. A pair of tie rods passes through all four platens. The first outer platen is attached to the ends of the tie rods. The second outer platen is moved by a mechanism such as a cylinder or toggle mechanism for movement on the tie rods. The first inner platen is connected to the second outer platen by a second set of tie rods. The second inner platen is connected to the first outer platen by a third set of tie rods. When the first assembly of open blow mold sets is brought into position adjacent the extruder station, parisons are extruded between both sets of mold halves. The first assembly of mold sets is closed about the parisons and then moved to one of the blow stations. As the first assembly of mold sets moves away from the extruder means, the second assembly of mold sets at the other blow station is opened, releasing the containers which have been blown at the other station and the second assembly of open blow mold halves are moved to the extruder station for a continuation of the cycle.